max 10: Alternate between two clock sources without reseting I/Os values ??

Most PLLs have a clock switchover function, which is where I would start. (I don't remember if M10 has this or not). This could get complicated in that when switching the PLL has to lock to the second clock, where I don't know if your system can tolerate that. Also, if the clocks are not close in frequency, the PLL would have to be reconfigured, which can be a pain.

I believe you can also have two clocks come in and do this in logic. It's not "recommended" but certainly works. I have an Arria 10 design with 12 clock muxes in logic that then drive globals, and it's all working in hardware, so it is do-able.